The present invention relates to variable valve mechanisms of internal combustion engines.
Conventional internal combustion engines utilize two throttling devices, i.e., a throttle valve and the intake valves of the engine. The throttle valve is actuated by a driver depressing and/or releasing the gas pedal, and regulates the air flow to the intake valves. The engine intake valves are driven by the camshaft of the engine. The intake valves open and close at predetermined angles of camshaft rotation to allow the descending piston to draw air into the combustion chamber. The opening and closing angles of the valves and the amount of valve lift is fixed by the cam lobes of the camshaft. The valve lift profile (i.e., the curve of valve lift plotted relative to rotation of the camshaft) of a conventional engine is generally parabolic in shape.
Modern internal combustion engines may incorporate more complex and technologically advanced throttle control systems, such as, for example, an intake valve throttle control system. Intake valve throttle control systems, in general, control the flow of gas and air into and out of the cylinders of an engine by varying the timing and/or lift (i.e., the valve lift profile) of the intake valves in response to engine operating parameters, such as, for example, engine load, speed, and driver input. Intake valve throttle control systems vary the valve lift profile through the use of various mechanical and/or electromechanical configurations, generally referred to herein as variable valve mechanisms. Examples of variable valve mechanisms are detailed in commonly-assigned U.S. Pat. No. 5,937,809, the disclosure of which is incorporated herein by reference.
Conventional variable valve mechanisms typically include many component parts, such as link arms, joints, pins and return springs, and are thus relatively complex mechanically. The many component parts increase the cost of the mechanism and make the mechanism more difficult to assemble and manufacture. The joints and pins of a conventional variable valve mechanism are subject to interfacial frictional forces which negatively impact durability and efficiency. The use of return springs negatively impact the durability and limit the operating range of conventional variable valve mechanisms, thereby limiting the operation of the intake valve throttle control system to a correspondingly-limited range of engine operation.
Therefore, what is needed in the art is a variable valve mechanism having fewer component parts, thereby reducing cost and complexity of the mechanism.
Furthermore, what is needed in the art is a variable valve mechanism with fewer joints and/or pins, thereby reducing frictional losses in and increasing the durability of the mechanism.
Moreover, what is needed in the art is a variable valve mechanism that eliminates the use of return springs, thereby increasing the operating range of the mechanism and correspondingly increasing the engine operating range of the intake valve throttle control system.
The present invention provides a variable valve mechanism for an internal combustion engine.
The invention comprises, in one form thereof, an elongate input shaft having a central axis. An input cam lobe is disposed on the input shaft and is eccentric relative to the central axis. A guide member is pivotally mounted on the input shaft. A frame is disposed in engagement with the input cam lobe, and is pivotally and slidably coupled to the guide member. A link has a first end pivotally coupled to the frame. An output cam is pivotally mounted on the input shaft. The output cam is pivotally coupled to a second end of the link arm. The output cam is configured for oscillating engagement of a roller of a roller finger follower.
An advantage of the present invention is that fewer component parts are used relative to a conventional variable valve mechanism, thereby reducing the cost and complexity of the mechanism.
Another advantage of the present invention is that fewer joints/pins are necessary relative to a conventional variable valve mechanism, thereby reducing friction and increasing durability of the mechanism.
A still further advantage of the present invention is no return springs are used, thereby further increasing the durability of the mechanism and enabling use of the mechanism over a wider range of engine operating conditions.